The August issue of SFX magazine has an interview with Aaron Douglas in which the actor gives away massive, massive spoilers about one of the deepest mysteries of the show (though not the identity of the final Cylon, to be sure - it's more important than that). Unless Aaron is bullshitting us (seems unlikely in an interview published in a fairly well-known magazine), this explains a thing or 2 about the Cylons. I don't have the issue, but someone on another forum kindly provided this description (and a bit of speculation about it):
(be sure you want to read this before you do)
Apparently the situation was that the original Cylons were created on Kobol to serve the humans there, 4,000+ years ago, and evolved a humanoid faction like the later Cylons. There was a war that partially devastated the planet, splintering the people into twelve factions or colonies, plus the Cylons as the thirteenth (it's unclear if this was an intercine human war or another robotic rebellion). The Cylons took off into space on their own, but it seems they were on better terms with the humans of the other colonies and left messages for them. The Cylons went and set up home on another planet: Earth. The other humans later left Kobol and went to settle the Twelve Colonies and all contact was lost. The Cylons of Earth built up a civilisation there, but fell into warfare of their own and devastated the planet some decades ago. At least four survived (he doesn't bring the fifth up at all) and travelled to the Twelve Colonies to find out why humans and their creations have this self-destructive streak to them. They 'switched off' their Cylon sides (with a failsafe that they would 'wake up' if they got close to Earth again) and went to live amongst the humans. Apparently the Final Five are very interested in the Cycle of Time and believed they could better understand it by becoming human.
No explanation is given for how three of them ended up on Galactica and the fourth on Caprica as one of the handful of survivors. No explanation is given for how the modern Cylons have myths and legends about the Final Five (although a logical exrapolation is that the FF were involved in the creation of this generation of Cylons, or perhaps their programming). No explanation is given for the large age gap between Tigh and Tory/Anders/Tyrol either. There is also no confirmation that the Earth in the show is 'our' Earth, a parallel reality Earth or whatever. My guess is that no relationship will be shown between the real world and Earth in the show: it will be left vague, with the possibility that Earth in the show is our world many, many thousands of years into the futuere after humans have left Earth, gone to Kobol etc.
Some comments of my own:
We did see the "real" Earth in Crossroads - with America clearly visible. I suspect this planet will turn out to be "the promised land", "new Earth" and what they call Earth in the show will be what they call Earth, in-show.
The spoilers are consistent with a much earlier one (from Ausiello) that said the name of the 13th tribe was "Cylon". Given that technology like the Hub appears to be a one off, I would not be surprised if this technology was inherited from the 13th tribe, and the humanoid Cylons, at least, are copies (technology-wise) of the Cylons of the 13th tribe.